1. Field of the Invention
The present invention relates to a recording/reproducing method of a magnetic tape in a tracking servo system, using a multi-channel type head unit comprising a plurality of data heads for recording/reproduction.
2. Description of the Related Art
There are a variety of uses of a magnetic tape, including uses as an audio tape, a video tape and a computer tape. Particularly in the field of computer data backup tapes, a recording capacity has been increased with increase in capacity of a hard disc as a backup target. One of means for increasing the capacity of a magnetic tape is narrowing the width of each data track to increase the number of the data tracks, the so-called increase in recording density of data tracks.
In increasing a recording density of data tracks, it is essential to introduce a recording/reproducing technique named a so-called tracking servo system. The tracking servo system here refers to a technique in which servo tracks consisting of servo signals previously written on a magnetic tape are read with servo heads provided on a head unit, and in response to the read signals, the positional shift of the head unit in the width direction of the magnetic tape is controlled, to allow data heads to follow corresponding data tracks. According to this tracking servo system, even when the magnetic tape vibrates in the width direction in recording/reproduction to lead to displacement of the data tracks, the vibration of the magnetic tape is detected from changes in signals of the servo heads which are tracking signals from the servo tracks, and according to these changes, recording heads can be led onto the data tracks, thereby enabling significant improvement in recording/reproduction accuracy.
Conventional examples of such a tracking servo system are described in Japanese Laid-Open Patent Publication No. 2002-157722, Japanese Laid-Open Patent Publication No. 2003-173508, and the like. In Japanese Laid-Open Patent Publication No. 2002-157722, in addition to normal servo heads, pre-reading servo heads are provided for reading positional information of servo tracks prior to reading by the normal servo heads so that tracking servo accuracy can be improved. In Japanese Laid-Open Patent Publication No. 2003-173508, a servo signal for fine movement written in each data track on a magnetic tape is read with a magnetic head, and based upon the read signal, an actuator for fine movement built in each magnetic head is driven to control fine movements of a recording head and a reproducing head individually, so that tracking servo accuracy can be improved.